Scientists Aim To Improve Photosynthesis 156
vasanth writes "Two new initiatives at the University of Cambridge aim to address the growing demand on the Earth's resources for food and fuel by improving the process of photosynthesis. Four transatlantic research teams – two of which include academics from Cambridge's Department of Plant Sciences – will explore ways to overcome limitations in photosynthesis which could then lead to ways of significantly increasing the yield of important crops for food production or sustainable bioenergy. Despite the fact that photosynthesis is the basis of energy capture from the sun in plants, algae and other organisms, it has some fundamental limitations. There are trade-offs in nature which mean that photosynthesis is not as efficient as it could be – for many important crops such as wheat, barley, potatoes and sugar beet, the theoretical maximum is only 5%, depending on how it is measured. There is scope to improve it for processes useful to us, for example increasing the amount of food crop or energy biomass a plant can produce from the same amount of sunlight."
Re:New Pigments! (Score:5, Informative)
The photosystem is pretty good at capturing photons! It's after that initial step that the tough bits of chemistry come in.
First up, whenever you capture energy, you will heat up, hence plants have to manage that, and they do that with radiating out the excess energy captured (it is a lot!). There are a bunch of publications on reducing chlorophyll quantity in algae, which led to an improvement in photosynthetic efficiency and a drop in the excess energy radiated out (I think it was in the red region).
After that, the captured energy is used to split water, generating rather damaging radicals/ions (I forget which one) in the process - one changes your pH, the other causes redox stress. Either way, both are bad. The photo-system can't take a lot of that either, hence there are a ridiculous number of processes to effectively convert the split water back to water! (Refer Dynamics of Photosynthesis - Annual Review by Eberhard et al... Hah, luckily remember one paper from my thesis work!)
It doesn't get much better by the time the Hydrogen ion travels across the membranes, creating the much wanted NADPH, and some ATPs in the process. Now, depending on the chemicals wanted by the cells, the ratio of NADPH/ATP need to be tweaked, losing some energy there too.
And then come in the enzymes which start to use this simple energy to climb up the rather hard entropy ladder to create ordered polymers from the ridiculously simple water and carbon dioxide. Not the easiest of tasks in my opinion... and my un-calculated and un-verified bias is that the free energy change needed to accomplish this must be pretty high. Thermodynamics didn't like me very much... Nonetheless, the often abused number of 5% or 10% or 1% (yes, you can find all of these numbers in literature) photosynthetic efficiency means little as people always compare sunlight received to the calorific value of the biomass, completely missing out all the effort it took to build up that complexity against the rather real forces of disorder. Burning it is a complete waste!
Which is why my money (when I will have money!) will be on chemically simpler fuels - higher efficiencies are possible. But unfortunately, none of our alternatives to biomass have the self-replicating chemistry awesomeness of Biology. Hence it's not very cheap to manufacture and maintain. Plants kind of grow... You don't have to do much. Except, of course, if you're a corn ethanol producer, where you're doing too much! ;)
So basically, the problems are not at the pigments... The quantum yield of photon capture is near 100%. The complexity is after that. It's a mix of matching rates of various processes along the way, and losing energy working against entropy. And we're not even *close* to figuring out this system. Long shot.
Sayash